In order to achieve the desired degree of surface finishing quality, it is often necessary to smooth or polish the surface of plastics and of dried and/or cured coatings of paints and like materials, particularly intermediate coats that are to be covered by another coating of paint or lacquer. This smoothing and/or polishing is most commonly accomplished by abrasive finishing or sanding, using an abrasive such as silicon carbide, garnet, iron oxide, or aluminum oxide, either in the form of a coated abrasive in which the abrasive grits are attached to some flexible backing or in a slurry of the abrasive grits with some liquid. If a coated abrasive is used, it is customary to utilize a liquid auxiliary during the sanding operation, in order to achieve optimum surface quality and avoid the generation of excessive dust, which would at best be annoying, and at worst could be seriously hazardous, to workers performing the sanding; dust could also damage wet protective coating materials on processed parts in the vicinity of the sanding operation by settling on the wet coatings and thereby making the surface rough when it is desired to be smooth. Therefore, whether a coated abrasive or a slurry is used initially, by the completion of the sanding operation the smoothed surface is normally covered with a mixture of a liquid carrier and suspended finely divided abrasive and solid organic particles. This mixture is commonly called "sanding mud" or simply "mud" in the abrasive art.
Before subsequent finishing operations, the sanding mud normally should be removed from the surface. Water or a water based rinse liquid is usually used to accomplish this removal, and sometimes power washing of the rinse liquid is used to assist in removing the sanding mud. In many instances, not even power washing will satisfactorily remove the sanding mud, so that hand rubbing or wiping, with substantial expense that would preferably be avoided, is required in order to achieve adequate surface quality.
In many instances in the prior art, a mixture of isopropyl alcohol (hereinafter often abbreviated "IPA") or a conventional dishwashing detergent liquid and water has been used as the sanding liquid auxiliary; water without any special additive is also frequently used. These types of liquid auxiliary have proved to be at least moderately satisfactory when the sanding mud formed in the course of using it is promptly washed away after completion of sanding. However, in certain assembly line manufacturing operations, it has been found that the time between sanding and washing is long enough for the sanding mud formed during use of these types of liquid auxiliary to dry sufficiently to resist ready removal by rinsing, or even by power washing, with water. Even in manufacturing operations where such drying does not occur during operation under most conditions, it can still occur during interruptions of normal processing conditions, such as occur during rest periods for the operators, which may include as much as two-thirds of the time in a day in single worker shift operations, or as a result of mechanical malfunctions of the operations. Also, IPA is of course a regulated VOC. Accordingly, a major object of this invention is to provide a superior aqueous liquid auxiliary for sanding that is substantially free from VOC's and is readily removed by water rinsing, even after substantial times of exposure to normal ambient air. Another object is to provide a technically satisfactory aqueous liquid auxiliary containing only ingredients that are harmless to human skin, in view of the virtual practical impossibility of preventing contact between the liquid auxiliary used in wet sanding by hand and the skin of the workers performing the sanding. Other objects will be apparent from the description below.